The accessories in a conventional motor vehicle are powered by output from the engine. A hybrid electro-mechanical vehicle generally includes both an internal combustion engine and one or more electric motor/generators. Some of the accessories in a hybrid vehicle may require power while the engine is off and the vehicle is being powered by the electric motor/generator. Traditionally, in order to power hybrid vehicle accessories when the engine is off, it was necessary to provide each such accessory with a separate electric motor.
The typical automotive accessory drive system consists of a drive pulley connected to an output shaft of the engine, typically the crankshaft. Wrapped around this pulley is a flexible drive belt, which in turn is wrapped around a plurality of driven pulleys. This flexible drive belt transmits drive forces between the drive pulley and the driven pulleys. The driven pulleys may be fixably attached to accessories known in the art such as a power steering pump, air conditioning compressor, alternator, and water pump.
A parallel electric hybrid vehicle includes a transmission adapted to receive the output power from either an engine or an electric motor, or both. Additionally, in a parallel electric hybrid vehicle the power supplied by the engine and the power supplied by the source of electrical energy are independently connected to the transmission thereby forming a “parallel” type connection.